Semiconductor device

ABSTRACT

A semiconductor device is provided. The semiconductor device includes an insulating structure and a dielectric structure. The insulating structure is disposed on a substrate and has a plurality of openings. The dielectric structure is disposed on the insulating structure and extending into the plurality of openings.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional application of and claims the priority benefit of U.S. application Ser. No. 15/476,751, filed on Mar. 31, 2017, now allowed, which claims the priority benefit of Taiwan application serial no. 106103493, filed on Feb. 2, 2017. The entirety of each of the above-mentioned patent applications is hereby incorporated by reference herein and made a part of the specification.

BACKGROUND OF THE INVENTION Field of Invention

The present invention relates to a semiconductor device.

Description of Related Art

A silicon-on-insulator (SOI) metal oxide semiconductor (MOS) device has the advantages of a high component density, a low threshold voltage, a small parasitic capacitance etc., so it has drawn more attention in the industry. However, during a process of fabricating a SOI MOS device, different device densities in respective regions on a substrate cause a loading effect and therefore a difficulty for the subsequent processes, and thus, the device reliability is affected.

SUMMARY OF THE INVENTION

Accordingly, the present invention provides a method of fabricating a semiconductor device, by which the loading effect caused by different device densities in respective regions on a substrate can be reduced, and the issues such as a difficulty in process and a low reliability can be avoided.

The present invention provides a semiconductor device that includes an insulating structure disposed on a substrate and having a plurality of openings, and a dielectric structure disposed on the insulating structure and extending into the plurality of openings.

According to an embodiment of the present invention, the semiconductor device further includes an etching stop layer interposed between the insulating structure and the dielectric structure.

According to an embodiment of the present invention, the etching stop layer further extends to cover sidewalls and bottoms of the plurality of openings.

According to an embodiment of the present invention, the dielectric structure includes a first patterned dielectric layer disposed on the etching stop layer, and a second dielectric layer disposed on the first patterned dielectric layer and extending into the plurality of openings.

According to an embodiment of the present invention, the insulating structure includes a first insulating layer disposed on the substrate, and a second insulating layer having the plurality of openings and disposed between the first insulating layer and the etching stop layer.

According to an embodiment of the present invention, the dielectric structure in each of the plurality of openings has an inverted-Y shaped interface.

According to an embodiment of the present invention, the dielectric structure in the plurality of openings has a plurality of air gaps.

According to an embodiment of the present invention, the semiconductor device further includes an element disposed on the dielectric structure.

According to an embodiment of the present invention, the element includes an inductor, a ground-signal-ground (GSG) pad or a combination thereof.

In view of the above, during the method of fabricating a device of the invention, dummy patterns and optional dummy gates are formed on a substrate in a sparse area, so the sparse area has a density or hardness comparable to that of the dense area. Therefore, during the subsequent polishing process, the loading effect caused by different device densities in respective regions on the substrate can be avoided. The dummy patterns and dummy gates are then removed from the sparse area before the subsequent processes for the device are performed. Thus, the device performance is not affected by the dummy gates since the dummy gates do not remain on the substrate.

In order to make the aforementioned and other objects, features and advantages of the present invention comprehensible, a preferred embodiment accompanied with figures is described in detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.

FIG. 1A to FIG. 1H are cross-sectional views of a method of fabricating a semiconductor device in accordance with a first embodiment of the concept of the present invention.

FIG. 1I is a cross-sectional view of a semiconductor device formed by applying the method in accordance with the first embodiment of the concept of the present invention.

FIG. 2A to FIG. 2F are cross-sectional views of a method of fabricating a semiconductor device in accordance with a second embodiment of the concept of the present invention.

FIG. 2G is a cross-sectional view of a semiconductor device formed by applying the method in accordance with the second embodiment of the concept of the present invention.

FIG. 3A to FIG. 3G are cross-sectional views of a method of fabricating a semiconductor device in accordance with a third embodiment of the concept of the present invention.

FIG. 3H is a cross-sectional view of a semiconductor device formed by applying the method in accordance with the third embodiment of the concept of the present invention.

FIG. 4A to FIG. 4F are cross-sectional views of a method of fabricating a semiconductor device in accordance with a fourth embodiment of the concept of the present invention.

FIG. 4G is a cross-sectional view of a semiconductor device formed by applying the method in accordance with the fourth embodiment of the concept of the present invention.

FIG. 5 is a top view of a sparse area according to an embodiment of the present invention.

FIG. 6A to FIG. 6F are cross-sectional views of a method of fabricating a semiconductor device in accordance with a fifth embodiment of the concept of the present invention.

FIG. 6G is a cross-sectional view of a semiconductor device formed by applying the method in accordance with the fifth embodiment of the concept of the present invention.

DESCRIPTION OF EMBODIMENTS

The present invention may be embodied in various forms and is not limited to the embodiments described herein. For the sake of clarity, the same reference numbers are used in the drawings and the description to refer to the same or like parts.

FIG. 1A to FIG. 1H are cross-sectional views of a method of fabricating a semiconductor device in accordance with a first embodiment of the concept of the present invention.

Referring to FIG. 1A, a semiconductor-on-insulator (SOI) substrate 20 is provided. The SOI substrate 20 includes, from bottom to top, a substrate 11, a first insulating layer 10 and a semiconductor layer 9. The substrate 11 includes silicon. The first insulating layer 10 includes silicon oxide. The first insulating layer 10 is buried between the substrate 11 and the semiconductor layer 9, so it is called a buried insulating layer. The semiconductor layer 9 includes silicon, such as monocrystalline silicon. The semiconductor layer 9 is provided with a dopant therein or free of dopants. The dopant can be a P-type or N-type dopant. The P-type dopant includes boron. The N-type dopant includes phosphor or arsenic.

Thereafter, a patterned mask layer 8 is formed on the semiconductor layer 9. The patterned mask layer 8 includes a photoresist material. The method of forming the patterned mask layer 8 includes forming a photoresist layer on the SOI substrate 20, and preforming exposure and development steps to the photoresist layer.

Referring to FIG. 1B, an etching process is performed to the semiconductor layer 9 by using the patterned mask layer 8 as a mask, so as to form a plurality of dummy patterns 9 a. The patterned mask layer 8 is then removed. The plurality of dummy patterns 9 a can be distributed evenly or unevenly. As shown in FIG. 5, when the dummy patterns 9 a are distributed evenly, each of the dummy patterns 9 a has the same size or shape, or the width of a gap 30 between any two adjacent dummy patterns 9 a is constant. When the dummy patterns 9 a are distributed unevenly, each of the dummy patterns 9 a has a different size or shape, or the width of a gap 30 between any two adjacent dummy patterns 9 a is not constant. The dummy patterns 9 a can be distributed regularly or irregularly. The dummy patterns 9 a can be distributed in a regular manner. For example, the size or shape of each dummy pattern 9 a, or the width of a gap 30 between any two adjacent dummy patterns 9 a can be adjusted by a predetermined rule. The dummy patterns 9 a can be distributed in an irregular manner. For example, the size or shape of each dummy pattern 9 a, or the width of a gap 30 between any two adjacent dummy patterns 9 a can be adjusted irregularly. In some embodiments, the dummy patterns 9 a can be separated from each other. Each of the dummy patterns 9 a can have a regular or irregular shape. The regular shape can be a block, a strip or a combination thereof. The block may be circular, oval, triangular, square, rectangular (as shown in FIG. 5), polygonal trapezoidal or a combination thereof. The strip may be straight, wavy, serpentine or a combination thereof. In alternative embodiments, the dummy patterns 9 a can be connected to form a mesh. In other words, the gaps 30 may be circular, oval, triangular, square, rectangular, polygonal trapezoidal or a combination thereof. The gaps 30 can formed as strips. The strips can be straight, wavy, serpentine or a combination thereof.

Thereafter, as shown in FIG. 1B and FIG. 1C, a second insulating layer 12 is formed around the plurality of dummy patterns 9 a. The second insulating layer 12 includes a material the same as or different from that of the first insulating layer 10. The second insulating layer 12 includes silicon oxide, silicon nitride or a combination thereof. In some embodiments, the method of forming the second insulating layer 12 includes the following steps. A second insulating material layer (not shown) is forming on the SOI substrate 20 by a chemical vapour deposition (CVD) process or a spin coating process. The second insulating material layer is formed on the dummy patterns 9 a and fills into the gaps 30 between the dummy patterns 9 a. Thereafter, a chemical mechanical polishing (CMP) process or an etching back process is performed by using the dummy patterns 9 a as stop layers, so as to remove the second insulating material layer on the dummy patterns 9 a. In some embodiments, the surface of the second insulating layer 12 is substantially coplanar with the surfaces of the dummy patterns 9 a.

Referring to FIG. 1D, a gate dielectric layer 7 is formed on the dummy patterns 9 a and the second insulating layer 12. The gate dielectric layer 7 includes silicon oxide, silicon nitride or a high-k material. The high-k material has a dielectric constant greater than 4, greater than 7 or even greater than 10. The high-k material can be metal oxide, such as rare earth metal oxide. For example, the high-k material includes hafnium oxide (HfO₂), hafnium silicon oxide (HfSiO), hafnium silicon oxynitride (HfSiON), aluminum oxide (Al₂O₃), yttrium oxide (Y₂O₃), lanthanum oxide (La₂O₃), lanthanum aluminum oxide (LaAlO), tantalum oxide (Ta₂O₅), zirconium oxide (ZrO₂), zirconium silicon oxide (ZrSiO₄), hafnium zirconium oxide (HfZrO), strontium bismuth tantalate (SrBi₂Ta₂O₉; SBT) or a combination thereof. The method of forming the gate dielectric layer 7 includes performing a CVD process.

Continue referring to FIG. 1D, a conductive layer 13 is formed on the gate dielectric layer 7. The conductive layer 13 can be a single layer, a dual-layer structure or a multi-layer material structure. The conductive layer 13 includes a semiconductor material, a metal material, a metal alloy material or a combination thereof. The semiconductor material includes doped polysilicon, undoped polysilicon, amorphous silicon, a SiGe material or a combination thereof. The metal material includes a metal or a metal compound, such as copper, aluminum, tantalum, tungsten, tantalum nitride or titanium nitride. The metal alloy material includes tungsten, titanium, cobalt, an alloy made of nickel and polysilicon or a copper-aluminum alloy. The method of forming the conductive layer 13 includes performing a CVD or PVD process.

Still referring to FIG. 1D, a patterned mask layer 14 is formed on the conductive layer 13. The positions of patterns of the patterned mask layer 14 correspond to the positions of the dummy patterns 9 a. In some embodiments, the patterns of the patterned mask layer 14 and the dummy patterns 9 a have substantially the same or similar shape. In an exemplary embodiment, the patterns of the patterned mask layer 14 and the dummy patterns 9 a have the same shape, but the patterns of the patterned mask layer 14 have a dimension (e.g., width) smaller than that of the dummy patterns 9 a. In alternative embodiments, the patterns of the patterned mask layer 14 and the dummy patterns 9 a have substantially different shapes. In an exemplary embodiment, the patterns of the patterned mask layer 14 and the dummy patterns 9 a have different shapes, the patterns of the patterned mask layer 14 have a dimension (e.g., width) smaller than that of the dummy patterns 9 a, and the boundary of each pattern of the patterned mask layer 14 is within the boundary of the corresponding dummy pattern 9 a. The method of forming the patterned mask layer 14 includes forming a photoresist layer, and then preforming exposure and development steps to the photoresist layer.

Referring to FIG. 1E, an etching process is performed to the conductive layer 13 by using the patterned mask layer 14 as a mask, so as to form a plurality of dummy gates 13 a. The patterned mask layer 14 is then removed. The dummy gates 13 a are disposed over the dummy patterns 9 a, and the positions of the dummy gates 13 a correspond to the positions of the dummy patterns 9 a. In some embodiments, the dummy gates 13 a and the dummy patterns 9 a have the same shape, but the dummy gates 13 a have a dimension (e.g., width) smaller than that of the dummy patterns 9 a. In some embodiments, the dummy gates 13 a and the dummy patterns 9 a have different shapes, the dummy gates 13 a have a dimension (e.g., width) smaller than that of the dummy patterns 9 a, and the boundary of each dummy pattern 9 a is within the boundary of the corresponding dummy pattern 9 a.

Referring to FIG. 1F, an etching stop layer 15 is formed on the gate dielectric layer 7 and the dummy gates 13 a, and covers the gate dielectric layer 7 and the tops and sidewalls of the dummy gates 13 a. In some embodiments, the shape of the etching stop layer 15 is a combination of successive U shapes and inverted U shapes arranged alternately. The etching stop layer 15 includes a material different from that of the first insulating layer 12. The etching stop layer 15 includes an insulating material, such as silicon oxide, silicon nitride, silicon oxynitride or a combination thereof. The method of forming the etching stop layer 15 includes performing a CVD process.

Thereafter, a patterned mask layer 6 is formed on the etching stop layer 15. The patterned mask layer 6 can be a patterned photoresist layer. The patterned mask layer 6 has a plurality of openings 31. The positions of the openings 31 correspond to the positions of the dummy patterns 9 a, and the openings 31 at least expose the etching stop layer 15 on the dummy patterns 9 a. In some embodiments, the openings 31 of the patterned mask layer 6 and the dummy patterns 9 a have substantially the same or similar shape. In an exemplary embodiment, the openings 31 of the patterned mask layer 6 and the dummy patterns 9 a have the same shape, but the openings 31 of the patterned mask layer 6 have a dimension (e.g., width) equal to or greater than that of the dummy patterns 9 a.

Referring to FIG. 1F, FIG. 1G and FIG. 5, an etching process is performed to the etching stop layer 15 exposed by the openings 31 and to the underlying gate dielectric layer 7 and the dummy patterns 9 a by using the patterned mask layer 6 as a mask, so as to form an etching stop layer 15 a with openings 16, a gate dielectric layer 7 a and a second insulating layer 12. The patterned mask layer 6 is then removed. The bottoms of the openings 16 expose the first insulating layer 10, and the sidewalls of the openings 16 expose the etching stop layer 15 a, the gate dielectric layer 7 a and the second insulating layer 12. The first insulating layer 10 and the second insulating layer 12 form an insulating structure 21 having the openings 16. The openings 16 have a width W2, and the dummy patterns 9 a have a width W1 (FIG. 1B). In some embodiments, W2≥W1. Two adjacent openings 16 are separated by a distance S1. In some embodiments, the distance S1 can be greater than 0.4 μm. In other words, the patterned mask layer 6 in FIG. 1F can be formed by exposing a photoresist layer with a low-cost photomask and developing the exposed photoresist layer.

Referring to FIG. 1G and FIG. 1H, a dielectric structure 22 is formed on the substrate 11. The dielectric structure 22 fills into the openings 16. The dielectric structure 22 can include a single layer, a dual-layer structure or a multi-layer structure. In some embodiments, the dielectric structure 22 can be an inter-layer dielectric (ILD) layer. In alternative embodiments, the dielectric structure 22 can include an inter-layer dielectric (ILD) layer and an inter-metal dielectric (IMD) layer. The dielectric structure 22 includes silicon oxide, silicon nitride, a low-k material having a dielectric constant less than 4 or a combination thereof. The low-k material includes hydrogen silsesquioxane (HSQ) or methylsilsesquioxan (MSQ). The method of forming the dielectric structure 22 includes performing a CVD process or a spin coating process. The dielectric structure 22 has a thickness D, and W2≤2D.

Continue referring to FIG. 1H, the dielectric structure 22 extends into the openings 16, and covers the surface and sidewall of the etching stop layer 15 a, the sidewalls of the gate dielectric layer 7 a and the second insulating layer 12, and the surface of the first insulating layer 10. In some embodiments, the dielectric structure 22 in each of the openings 16 has an inverted-Y shaped interface. In alternative embodiments, the dielectric structure 22 formed in the openings 16 has a plurality of air gaps 32 therein.

The method of the first embodiment describe above can be applied to the method of forming a sparse area of a semiconductor device having different device intensities. FIG. 1I is a cross-sectional view of a semiconductor device formed by applying the method in accordance with the first embodiment of the concept of the present invention.

Referring to FIG. 1I, the substrate 11 includes a sparse area 5 a and a dense area 5 b. The sparse area 5 a can have a structure as shown in FIG. 1H.

Referring to FIG. 1I, in the sparse area 5 a, the substrate 11 has a first insulating layer 10 thereon. The first insulating layer 10 has a plurality of protruding structures 23 thereon. The protruding structures 23 include a second insulating layer 12, a gate dielectric layer 7 a and an etching stop layer 15 a. In some embodiments, the protruding structures 23 are discontinuous or not connected to each other. In alternative embodiments, the protruding structures 23 are continuous or connected to each other. An opening is between two adjacent protruding structures 23. A dielectric structure 22 is disposed on the first insulating layer 10 and fills into the openings 16. In other words, the dielectric structure 22 is engaged with the protruding structures 23. In some embodiments, the dielectric structure 22 in each of the openings 16 has an inverted-Y shaped interface. In alternative embodiments, the dielectric structure 22 in the openings 16 has a plurality of air gaps 32. The dielectric structure 22 can include a single layer, a dual-layer structure or a multi-layer structure. In some embodiments, the dielectric structure 22 can be an inter-layer dielectric (ILD) layer. In alternative embodiments, the dielectric structure 22 can include an inter-layer dielectric (ILD) layer and an inter-metal dielectric (IMD) layer. An element 24 a can be subsequently formed on the dielectric structure 22. The element 24 a can be a conductive layer. The conductive layer can be an inductor, but the present invention is not limited thereto. In an alternative embodiment, the element 24 a further includes a ground-signal-ground (GSG) pad or a combination of an inductor and a GSG pad.

Referring to FIG. 1I, in the dense area 5 b, a SOI substrate 20 includes, from bottom to top, a substrate 11, a first insulating layer 10 and a semiconductor layer 9. In other words, the semiconductor layer 9 is formed in the dense area 5 b but not in the sparse area 5 a. In some embodiments, the semiconductor layer 9 in the dense area 5 b is substantially as high as the second insulating layer 12 in the sparse area 5 a, and the surface of the semiconductor layer 9 in the dense area 5 b is substantially coplanar with the surface of the second insulating layer 12 in the sparse area 5 a.

The SOI substrate 20 has a MOS effect transistor 34 formed thereon. The MOS effect transistor 34 includes a gate dielectric layer 7 b, a gate 13 b and doped regions 33. The gate dielectric layer 7 b and the gate dielectric layer 7 a can be formed simultaneously by performing the same patterning step (FIG. 1G) to the same gate dielectric layer 7 (FIG. 1D). The gate 13 b and the dummy gates 13 a (FIG. 1E) can be formed simultaneously by performing the same patterning step (FIG. 1E) to the same conductive layer 13 (FIG. 1D). The SOI substrate 20 has an etching stop layer 15 b and a dielectric structure 22 formed on the MOS effect transistor 34. The etching stop layer 15 b in the dense area 5 b and the etching stop layer 15 a in the sparse area 5 a can be formed simultaneously by performing the same patterning step (FIG. 1G) to the same etching stop layer 15 (FIG. 1F). A conductive wire 24 b is formed on the dielectric structure 22. The conductive wire 24 b is electrically connected to the doped regions 33 via a contact plug 25 that penetrates through the dielectric structure 22 and the etching stop layer 15 b. The conductive wire (or called a metal wire) 24 b and the element 24 a can be formed simultaneously by performing the same patterning step to the same conductive layer. The conductive layer includes a metal material, a metal alloy material or a combination thereof. The metal material includes a metal or a metal compound, such as copper, aluminum, tantalum, tungsten, tantalum nitride or titanium nitride. The metal alloy material includes tungsten, titanium, cobalt, an alloy made of nickel and polysilicon or a copper-aluminum alloy. The method of forming the conductive layer includes performing a CVD or PVD process.

In some embodiments, in addition to the contact plug 25, a multi-layer conductive wire structure (or called a multi-layer metal wire structure) and vias (not shown) can be further formed in the dielectric structure 22 in the dense area 5 b. However, in the sparse area 5 a, the dielectric structure 22 disposed below the element 24 a can be formed without contact plugs, conductive wires (or called a multi-layer metal wire structure) and vias. Alternatively, the number of layers of conductive wires (or called a multi-layer metal wire structure) and vias in the spares area 5 a is less than the number of layers of conductive wires (or called a multi-layer metal wire structure) and vias in the dense area 5 b.

FIG. 2A to FIG. 2F are cross-sectional views of a method of fabricating a semiconductor device in accordance with a second embodiment of the concept of the present invention. FIG. 2G is a cross-sectional view of a semiconductor device formed by applying the method in accordance with the second embodiment of the concept of the present invention.

Referring to FIG. 2A to FIG. 2G, the method of the second embodiment is similar to that of the first embodiment, and the difference between them lies in that the etching stop layer 15 (FIG. 2D) is directly formed on the dummy patterns 9 a and the second insulating layer 12. In other words, the gate dielectric layer 7 and the conductive layer 13 are not present between the etching stop layer 15 and the dummy patterns 9 a. Alternatively, the gate dielectric layer 7 and the conductive layer 13 as shown in FIG. 1D are formed on the dummy patterns 9 a and second insulating layer 12, but are then removed before forming the etching stop layer 15. Thereafter, an etching process is performed by using the patterned mask layer 6 as a mask, and the formed etching stop layer 15 a directly covers the second insulating layer 12 (FIG. 2E). In other words, as shown in FIG. 2F and FIG. 2G, the protruding structures 23 a include the second insulating layer 12 and the etching stop layer 15 a, but do not include the gate dielectric layer 7 a (FIG. 1H). The protruding structures 23 a are engaged with the dielectric structure 22.

FIG. 3A to FIG. 3G are cross-sectional views of a method of fabricating a semiconductor device in accordance with a third embodiment of the concept of the present invention. FIG. 3H is a cross-sectional view of a semiconductor device formed by applying the method in accordance with the third embodiment of the concept of the present invention.

Referring to FIG. 3A to FIG. 3G, the method of the third embodiment is similar to that of the second embodiment, and the difference between them lies in that the etching stop layer 15 (FIG. 3F) is formed after the dummy patterns 9 a are removed. In other words, the etching stop layer 15 is formed on the surface of the second insulating layer 12 and on the sidewalls and bottoms of the openings 16. The etching stop layer 15 is a continuous layer. In some embodiments, the shape of the etching stop layer 15 is a combination of continuous U shapes and inverted U shapes arranged alternately. In other words, as shown in FIG. 3F and FIG. 3G, the etching stop layer 15 is interposed between the insulating structure 21 and the dielectric structure 22. From another point of view, the etching stop layer 15 and the second insulating layer 12 form protruding structures 23 b, and the protruding structures 23 b are engaged with the dielectric structure 22.

FIG. 4A to FIG. 4F are cross-sectional views of a method of fabricating a semiconductor device in accordance with a fourth embodiment of the concept of the present invention. FIG. 4G is a cross-sectional view of a semiconductor device formed by applying the method in accordance with the fourth embodiment of the concept of the present invention.

Referring to FIG. 4A to FIG. 4D, steps similar to those of the first embodiment are performed, in which a semiconductor layer 9 of a SOI substrate 20 is patterned to form a plurality of dummy patterns 9 a, and a second insulating layer 12 is formed around the dummy patterns 9 a. Thereafter, an etching stop layer 15 is formed on the dummy patterns 9 a and the second insulating layer 12. The etching stop layer 15 is directly formed on the dummy patterns 9 a and the second insulating layer 12 (FIG. 4D). Similarly, the gate dielectric layer 7 and the conductive layer 13 (FIG. 1D) are not present between the etching stop layer 15 and the dummy patterns 9 a. Alternatively, the gate dielectric layer 7 and the conductive layer 13 as shown in FIG. 1D are formed on the dummy patterns 9 a and second insulating layer 12, but are then removed before forming the etching stop layer 15.

Continue referring to FIG. 4D, after forming the etching stop layer 15 and before forming a patterned mask layer 6, a first a dielectric layer 18 is formed on the etching stop layer 15. The first dielectric layer 18 includes silicon oxide, silicon nitride, a low-k material having a dielectric constant less than 4 or a combination thereof. The low-k material includes hydrogen silsesquioxane (HS Q) or methylsilsesquioxan (MSQ). The method of forming the first dielectric layer 18 includes performing a CVD process or a spin coating process.

Referring to FIG. 4D and FIG. 4E, after forming the patterned mask layer 6, an etching process is performed to the first dielectric layer 18, the etching stop layer 15 and the dummy patterns 9 a by using the patterned mask layer 6 as a mask, so as to form openings 16 through a first patterned dielectric layer 18 a, an etching stop layer 15 a and a second insulating layer 12. The patterned mask layer 6 is then removed. The bottoms of the openings 16 expose the first insulating layer 10. The sidewalls of the openings 16 expose the first patterned dielectric layer 18 a, the etching stop layer 15 a and the second insulating layer 12. The first insulating layer 10 and the second insulating layer 12 form an insulating structure 21 having the openings 16. The etching stop layer 15 a and the first patterned dielectric layer 18 a are disposed on the second insulating layer 12 of the insulating structure 21.

Referring to FIG. 4F, a second dielectric layer 17 is formed on the substrate 11. The second dielectric layer 17 and the first patterned dielectric layer 18 a includes the same material or different materials. The second dielectric layer 17 includes silicon oxide, silicon nitride, a low-k material having a dielectric constant less than 4 or a combination thereof. The low-k material includes hydrogen silsesquioxane (HSQ) or methylsilsesquioxan (MSQ). The method of forming the second dielectric layer 17 includes performing a CVD process or a spin coating process. The second dielectric layer 17 is disposed on the first patterned dielectric layer 18 a, extends into the openings 16, and covers the top and sidewall of the first patterned dielectric layer 18 a and the sidewalls of the etching stop layer 15 a and the second insulating layer 12. The second dielectric layer 17 and the first patterned dielectric layer 18 a form a dielectric structure 22. The etching stop layer 15 a is disposed between the insulating structure 21 and the dielectric structure 22. From another point of view, the etching stop layer 15 a and the second insulating layer 12 form a plurality of protruding structures 23 c, and the protruding structures 23 c are engaged with the dielectric structure 22.

In FIG. 4G, the dense area 5 b has a structure similar to that of FIG. 3H, and this structure further includes a first patterned dielectric layer 18 a disposed between the second dielectric layer 17 and the etching stop layer 15 a.

FIG. 6A to FIG. 6F are cross-sectional views of a method of fabricating a semiconductor device in accordance with a fifth embodiment of the concept of the present invention. FIG. 6G is a cross-sectional view of a semiconductor device formed by applying the method in accordance with the fifth embodiment of the concept of the present invention.

Referring to FIG. 6A to FIG. 6F, the method of the fifth embodiment is similar to that of the third embodiment, and the difference between them lies in that the etching stop layer 15 is not present between the insulating structure 21 and the dielectric structure 22. In other words, as shown in FIG. 6D and FIG. 6E, after removing the dummy patterns 9, the etching stop layer 15 is not formed. Alternatively, an etching stop layer 15 is formed and then removed. Therefore, in the sparse area 5 b of FIG. 6G, the etching stop layer 15 is not present between the insulating structure 21 and the dielectric structure 22. However, in the dense area 5 a, the remaining etching stop layer 15 b covers the MOS effect transistor 34.

In summary, during the method of fabricating a device of the invention, dummy patterns and optional dummy gates are formed on a substrate in a sparse area, so the sparse area has a density or hardness comparable to that of the dense area. Therefore, during the subsequent polishing process, the loading effect caused by different device densities in respective regions on the substrate can be avoided. The dummy patterns and dummy gates are then removed from the sparse area before the subsequent processes for the device are performed. Thus, the device performance is not affected by the dummy gates since the dummy gates do not remain on the substrate.

The present invention has been disclosed above in the preferred embodiments, but is not limited to those. It is known to persons skilled in the art that some modifications and innovations may be made without departing from the spirit and scope of the present invention. Therefore, the scope of the present invention should be defined by the following claims. 

What is claimed is:
 1. A semiconductor device, comprising: a substrate, having a dense area and a sparse area; a first insulating layer, disposed on the substrate in the dense area; a semiconductor layer, disposed on the first insulating layer in the dense area, wherein the substrate, the first insulating layer and the semiconductor layer in the dense area constitute a semiconductor-on-insulator (SOI) substrate; an insulating structure, disposed on the substrate in the sparse area and having a plurality of openings, wherein a top surface of the insulating structure is coplanar with a top surface of the semiconductor layer; a dielectric structure, disposed on the insulating structure and extending into the plurality of openings; and an etching stop layer, interposed between the insulating structure and the dielectric structure, wherein the first insulating layer is further disposed on the substrate in the sparse area, and the insulating structure comprises: the first insulating layer in the sparse area; and a second insulating layer, having the plurality of openings and disposed between the first insulating layer and the etching stop layer.
 2. The semiconductor device of claim 1, wherein the etching stop layer further extends to cover sidewalls and bottoms of the plurality of openings.
 3. The semiconductor device of claim 1, wherein the dielectric structure comprises: a first patterned dielectric layer, disposed on the etching stop layer; and a second dielectric layer, disposed on the first patterned dielectric layer and extending into the plurality of openings.
 4. The semiconductor device of claim 1, wherein the dielectric structure in each of the plurality of openings has an inverted-Y shaped interface.
 5. The semiconductor device of claim 1, wherein the dielectric structure in the plurality of openings has a plurality of air gaps.
 6. The semiconductor device of claim 1, further comprising an element disposed on the dielectric structure.
 7. The semiconductor device of claim 6, wherein the element comprises an inductor, a ground-signal-ground (GSG) pad or a combination thereof.
 8. The semiconductor device of claim 1, wherein the semiconductor layer is not disposed in the sparse area. 